Three classes of components are important in oxidative hair dyeing: primary intermediates, oxidants, and couplers. The primary intermediates are difunctional benzene derivatives capable of being oxidized with resultant development of color, e.g., ortho- and para-phenylenediamines and para-aminophenols.
Hydrogen peroxide is the usual oxidant, although persalts of various acids or solid organic peroxide adducts may be employed, especially where a solid oxidant is desired.
The third component type--the coupler--is important in hair coloring to produce color nuances necessary for the simulation of a natural hair color. Couplers do not undergo facile oxidation. Rather, it is believed that a coupler, which contains a strong electron donating group, provides a dye by reaction with electrophilic benzoquinoneimines. Thus, any aromatic compound having an amino or hydroxy group and an unblocked para position can react with a benzoquinoneimine to produce an indo dye. However, anilines and most monohydric phenols are usually insufficiently reactive to compete with the self-coupling reactions of the primary intermediates under hair dyeing conditions. For this reason, the most important couplers are phenols or anilines bearing a second strong electron donor in the meta position. See generally J. F. Corbett, The Role of Meta Difunctional Benzene Derivatives in Oxidative Hair Dyeing. I. Reaction With p-Diamines, J. Soc. Cosmet. Chem., 24, 103-134 (1973).
It is well known that the shade or color produced by a color coupler depends on its chemical nature. For example, with p-phenylenediamine as a primary intermediate, yellow to green/brown colors are produced by resorcinol couplers, red to red-violet colors are produced by m-aminophenol couplers and blue colors are produced by m-phenylenediamine and phenolic couplers.
In the important class of blue couplers, phenolic compounds in general form color far too slowly to be of practical commercial importance--the exception being 1-naphthol, which forms color at an acceptable rate, but has the disadvantage of poor solubility in hair dyeing systems, particularly in recently developed, highly aqueous systems. As an alternative, m-phenylenediamine couplers can be used. However, they have the disadvantage of producing dyes that slowly change color from blue to red over a period of days or weeks.
U.S. Pat. No. 4,797,130 to Clausen, et al. discloses compounds having the structures ##STR2## wherein the groups R.sup.1 and R.sup.2 may include hydrogen, alkyl, hydroxyalkyl, aminoalkyl, and the like. Unlike the dye coupler compounds of the present invention, the compounds (II) are primary intermediates, that is, color is developed by oxidizing these compounds, e.g., with hydrogen peroxide, to form benzoquinoneimines that are reactive with a color-producing coupler. Placement of the hydroxy and amino groups para to each other is essential for these compounds (II) to behave as primary intermediates.
U.S. Pat. No. 3,210,252 to Blanke, et al. discloses 5-amino-2-methylphenol as a coupler. When this coupler is used to couple with p-phenylenediamine, a red-violet shade is obtained on hair.
U.S. Pat. No. 4,065,255 to Andrillon, et al. discloses a coupler of the structure ##STR3## wherein R is a hydroxyalkyl of 1-4 carbon atoms. A red-violet color is obtained on gray hair when the coupler (III) with R defined as hydroxyalkyl containing 1 to 4 carbons is reacted with p-phenylenediamine
U.S Pat. No. 4,588,410 to Konrad discloses couplers of the structure ##STR4## wherein R is hydrogen, methyl or hydroxyethyl. The compound (IV) is especially useful for providing red tones. More specifically, compound (IV) when R is hydrogen couples with p-phenylenediamine to give intense mahogany coloration on human hair.
U.S. Pat. No. 3,834,866 to Pum discloses 5-aminoguaiacol derivatives (V) useful as coupling agents ##STR5## wherein when R is hydrogen, a dark maroon shade is produced with p-phenylenediamine on white virgin hair.
U.S. Pat. No. 3,712,790 to Kalopissis, et al. discloses the coupler ##STR6## wherein R is hydrogen, alkyl, hydroxyalkyl, acyl, or N-alkylated or unsubstituted aminoalkyl or carbamylmethyl group, the alkyl groups of these radicals having 1-6 carbons.
U.S. Pat. No. 4,094,635 to Bugaut, et al. discloses m-aminophenol sulfonamide couplers in hair dye compositions. When reacted with p-phenylenediamine, a red-violet coloration on natural white hair is obtained.
It is apparent that m-aminophenols bearing a substituent ortho and para to the hydroxy and amino groups, respectively, produce red to red-violet colors with p-phenylenediamine. It is unexpected that when this substituent is an aminomethyl group, intense blue to blue-violet colors are obtained.